DRDO Multi tasking staff Model paper 8

Suppose ‘r’ is the rate of interest per annum;
Since the interest is compounded half yearly;
∴ R = r/2 and t = 3 years
∴ 3645 = 2560 × (1 + r/200)‌3
⇒ (1 + r/200)‌3 = 729/512
⇒ 1 + r/200 = 9/8
⇒ r/200 = 1/8
⇒ r = 200/8 = 25%
∴ Rate of interest per annum = 25%